ICSE Class 10 Physics 2019 Solved Paper

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Question : 49
Total: 74
A pendulum has a frequency of 4 vibrations per second. An observer starts the pendulum and fires a gun simultaneously. He hears the echo from the cliff after 6 vibrations of the pendulum. If the velocity of sound in air is 340m s, find the distance between the cliff and the observer.
Solution:  
Time taken for 4 vibrations of the pendulum =1 sec
Time taken for 1 vibrations of the pendulum =
1
4
sec

Time taken for 6 vibrations of the pendulum =
1
4
×6
=1.5 sec

We know,
v=
2d
t

or d=
vt
2

d=
340×1.5
2
=255m
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